Normally, a trench with a depth of more than 10 μm is defined as a deep trench. Deep trench structures are widely used in semiconductor manufacturing in nowadays. For example, a deep trench can function as an isolation module to isolate power MOS transistors with different operation voltages; a deep trench can also be used in a superjunction MOSFET as a P type pillar in an N type drift layer structure (or an N type pillar in a P type drift layer structure) to form a P-N depletion junction to balance the electric field, so that insulation breakdown can be prevented, and high breakdown voltage can be achieved.
Conventional manufacturing method of superjunction MOSFET structure includes: growing an N type epitaxial layer as a drift layer on a P type substrate; forming a deep trench in the N type epitaxial layer by plasma etching; tilling the deep trench with P type epitaxial film or P type polysilicon; planarize the surface of the deep trench by CMP process. Thus, a P-N junction structure with alternating N type and P type regions is formed, wherein the deep trench is functioned as a P-pillar, the N type epitaxial layers beside the deep trench are functioned as N-drift regions. A similar function can be achieved by exchanging the N type and P type silicons.
The above method may have the following problems. On one hand, since N drift and P pillar regions are both made of silicon, it is difficult to distinguish the P pillar from the N drift regions during the CMP process, as a result, it is impossible to carry out selective removal, and the polishing may cause damage to the active area and hence influence the device performance. On the other hand, as the substrate and the material filled in the deep trench have the same type, it is hard to control polishing stop point during the CMP process.